Wireless communications, including radio frequency identification (RFID) and other near field communication (NFC) protocols, are gaining in popularity for applications such as security, inventory management, access control, and the like. The number of smart phones that include RFID or NFC protocols is growing along with the various applications of passive or active transponders, such as RFID indicator circuits and NFC indicator circuits. Such indicator circuits include an antenna that modulates, and in some instances emits, a wireless communication signal that can be read by a reader, such as a smartphone. A parasitic capacitance, however, may form between the antenna and a ground plane. Parasitic capacitance, for example, may be particularly problematic when the antenna is placed on or near metal. The parasitic capacitance may reduce the antenna voltage of the antenna within the indicator circuit. As a result, the read range of the antenna may be reduced. In addition, the parasitic capacitance may detune the antenna from the antenna's specified frequency, such as 13.56 MHz. The antenna may need to be re-tuned and the re-tuning could be impracticable in certain situations.
Electrochemical cells, or batteries, are commonly used as electrical energy sources. A battery contains a negative electrode, typically called the anode, and a positive electrode, typically called the cathode. The anode contains an active material that can be oxidized. The cathode contains an active material that can be reduced. The anode active material is capable of reducing the cathode active material. A separator is disposed between the anode and cathode. An electrolyte is also included within the battery. The aforementioned components are generally disposed in a metal can.
Battery testers may be used to determine characteristics of a battery, such as the remaining battery capacity. An exemplary type of a common battery tester that is placed on batteries is known as a thermochromic-type tester. In a thermochromic battery tester, a circuit may be completed when a consumer manually depressing one or two button switches. Once the switch is depressed, the consumer has connected the battery to the thermochromic tester. The thermochromic tester may include a silver resistor, e.g., a flat silver layer that has a variable width so that the electrical resistance also varies along its length. As current travels through the silver resistor, the dissipated power generates heat that changes the color of a thermochromic ink display that is placed over the silver resistor. The thermochromic ink display may be arranged as a gauge to indicate the relative capacity of the battery. However, it is typically necessary for the consumer to inconveniently hold the battery and/or remove the battery from the device in order to test the battery using the battery tester.
Accordingly, there exists a need for an indicator circuit for wireless communication, for example RFID and/or NFC applications, that is decoupled from a ground plane. A communications system including such an indicator circuit may reduce or eliminate shorting between the antenna and the ground plane. In addition, the communications system including such an indicator circuit may eliminate any need to re-tune the antenna. In addition, the communications system including such an indicator circuit may reduce or eliminate interference from other metal parts that may function as the ground plane. An indicator circuit for wireless communications that is decoupled from a ground plane may also be incorporated within a battery tester. Any parasitic capacitance that may form as a result of the metal housing of the battery or other metal components, such as those within the device, may be reduced or eliminated. In either instance, the read range of the antenna within the indicator circuit may not be adversely affected by the ground plane/metal components when the antenna is near the ground plane/metal components.